Polyethylene Compositions

ABSTRACT

Provided are various compositions, including but not limited to a bimodal polyethylene composition having a density of 0.940 g/cc or more, the composition comprising a high molecular weight polyethylene component and a low molecular weight polyethylene component, wherein the composition qualifies as a PE 100 material such that in accordance with ISO 1167 a pipe formed from the composition that is subjected to internal pipe resistance has an extrapolated stress of 10 MPa or more when the internal pipe resistance curve is extrapolated to 50 or 100 years in accordance with ISO 9080:2003(E), and wherein the melt strength is greater than 18 cN.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Ser. No. 61/135,036, filed Jul.16, 2008, the disclosure of which is incorporated by reference in itsentirety.

FIELD OF INVENTION

Embodiments of the present invention generally relate to compositionscontaining polyethylene, particularly bimodal polyethylene compositions.

BACKGROUND

Ongoing efforts have been directed to making polyolefin pipecompositions, particularly high density polyethylene pipe compositions.A goal is for the resin to be made economically and efficiently, whileproviding a pipe with a desirable balance of properties.

U.S. Pat. Nos. 7,037,977, 6,090,893, and 7,193,017, and U.S. PatentApplication Publications Nos. US 2007/027611, US 2004/0157988, and US2005/0234197 relate to polyethylene pipe resins. There is a need for ahigh strength polyethylene composition exhibiting a desirable balance ofproperties including in a class of embodiments a higher melt strength.

SUMMARY

In accordance with one aspect of the invention, there is provided a highdensity bimodal polyethylene composition having a density of 0.940 g/ccor more, the composition comprising a high molecular weight polyethylenecomponent and a low molecular weight polyethylene component, wherein:the composition qualifies as a PE 100 material such that in accordancewith ISO 1167 a pipe formed from the composition that is subjected tointernal pipe resistance has an extrapolated stress of 10 MPa or morewhen the internal pipe resistance curve is extrapolated to 50 or 100years in accordance with ISO 9080:2003(E); and the composition has amelt strength is greater than 18 cN.

In one embodiment, the high and low molecular weight polyethylenecomponents are formed in a single reactor.

In one embodiment, the melt strength is greater than 20 cN. In anotherembodiment, the melt strength is greater than 22 cN.

In one embodiment, the complex viscosity at 0.01 s-1 is greater than3.5*105 Pa-s. In another embodiment, the complex viscosity at 0.1 s-1 isgreater than 1.5*105 Pa-s.

In one embodiment, the overall PDI is from 15 to 40.

In one embodiment, the high molecular weight component is present in anamount of 45 to 60 wt % based upon the total weight of the composition.

In one embodiment, the average molecular weight (Mw) of the lowmolecular weight polyethylene component is from 5,000 to 35,000.

In one embodiment, the average molecular weight (Mw) of the highmolecular weight polyethylene component is from 400,000 to 700,000.

In one embodiment, the ratio of the weight average molecular weight ofhigh molecular weight component to the weight average molecular weightof low molecular weight component (MwHMW:MwLMW) is 15 to 40:1.

In one embodiment, the FI (I₂₁) of the composition is from 4 to 10 g/10min.

In one embodiment, the high molecular weight polyethylene component hasa density of 0.945 or less.

In one embodiment, the low molecular weight polyethylene component has adensity of 0.940 or more.

In one embodiment, the high molecular weight polyethylene componentincludes a polyethylene that includes a comonomer being butene, hexene,octene, or mixtures thereof, wherein the comonomer is present in theamount of more than 1.0 wt % of the polyethylene.

In one embodiment, the low molecular weight polyethylene componentincludes a polyethylene that includes a comonomer being butene, hexene,octene, or mixtures thereof, wherein the comonomer is present in theamount of less than 3.0 wt % of the polyethylene.

In one embodiment, the extrapolated stress is 10.5 MPa or more whenextrapolated to 50 or 100 years in accordance with ISO 9080:2003(E).

In one embodiment, wherein the high and low molecular weightpolyethylene components are formed by gas phase polymerization.

In one embodiment, the high and low molecular weight polyethylenecomponents are formed by slurry phase polymerization.

In one embodiment, the composition is made from polymerization conductedin the presence of a bimodal catalyst system that includes a metallocenebased catalyst.

In one embodiment, the high and low molecular weight polyethylenecomponents are formed from polymerization conducted in the presence of abimodal catalyst system that comprisesbis(2-trymethylphenylamido)ethyl)amine zirconium dibenzyl.

In one embodiment, the high and low molecular weight polyethylenecomponents are formed from polymerization conducted in the presence of abimodal catalyst system that comprisesbis(2-(pentamethyl-phenylamido)ethyl)amine zirconium dibenzyl.

In one embodiment, the high and low molecular weight polyethylenecomponents are formed from polymerization conducted in the presence of abimodal catalyst system that comprises(pentamethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdichloride.

In one embodiment, the high and low molecular weight polyethylenecomponents are formed from polymerization conducted in the presence of abimodal catalyst system that comprises(tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdichloride or(tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdimethyl.

In one embodiment, the high and low molecular weight polyethylenecomponents are formed from polymerization conducted in the presence of abimodal catalyst system that comprisesbis(2-pentamethylphenylamido)ethyl)zirconium dibenzyl orbis(2-pentamethylphenylamido)ethyl)zirconium dimethyl.

Any of the catalysts disclosed above may be combined to form a bimodalor multimodal catalyst system as discussed in more detail below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the dynamic viscosity of three samplesaccording to a class of embodiments of the invention and of fivecommercial samples.

FIG. 2 is a graph showing the Rheotens melt strength versus pull-offspeed for two samples according to a class of embodiments of theinvention and of four commercial samples.

FIG. 3 is a graph showing a molecular weight distribution (MWD) curvetaken of a bimodal product (sample 1163-18-1) according to an embodimentof the invention, using the SEC technique described herein (GPC method).

DETAILED DESCRIPTION

Before the present compounds, components, compositions, and/or methodsare disclosed and described, it is to be understood that unlessotherwise indicated this invention is not limited to specific compounds,components, compositions, reactants, reaction conditions, ligands,metallocene structures, or the like, as such may vary, unless otherwisespecified. It is also to be understood that the terminology used hereinis for the purpose of describing particular embodiments only and is notintended to be limiting.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified. Thus, for example, reference to “aleaving group” as in a moiety “substituted with a leaving group”includes more than one leaving group, such that the moiety may besubstituted with two or more such groups. Similarly, reference to “ahalogen atom” as in a moiety “substituted with a halogen atom” includesmore than one halogen atom, such that the moiety may be substituted withtwo or more halogen atoms, reference to “a substituent” includes one ormore substituents, reference to “a ligand” includes one or more ligands,and the like.

For purposes of convenience, various specific test procedures areidentified for determining properties such as average molecular weight,extrapolated stress, polydispersity index (PDI), flow index (FI) andmelt flow ratio (MFR). However, when a person of ordinary skill readsthis patent and wishes to determine whether a composition or polymer hasa particular property identified in a claim, then any published orwell-recognized method or test procedure can be followed to determinethat property (although the specifically identified procedure ispreferred, and that any procedure specified in a claim is mandatory, notmerely preferred). Each claim should be construed to cover the resultsof any of such procedures, even to the extent different procedures mayyield different results or measurements. Thus, a person of ordinaryskill in the art is to expect experimental variations in measuredproperties that are reflected in the claims. All numerical values can beconsidered to be “about” or “approximately” the stated value, in view ofthe nature of testing in general.

Density is a physical property of a composition, is determined inaccordance with ASTM-D-1505, and is expressed as grams per cubiccentimeter (or grams per milliliter).

Except to the extent the actual density is specified, the term “highdensity” means any density of 0.940 g/cc or above, alternatively 0.945g/cc or above, alternatively 0.950 g/cc or above, and alternativelystill 0.960 g/cc or above, and an illustrative range of a high densitycomposition is from 0.945 g/cc to 0.967 g/cc.

The term “polyethylene” means a polymer made of at least 50%ethylene-derived units, preferably at least 70% ethylene-derived units,more preferably at least 80% ethylene-derived units, or 90%ethylene-derived units, or 95% ethylene-derived units, or even 100%ethylene-derived units. The polyethylene can thus be a homopolymer or acopolymer, including a terpolymer, having other monomeric units. Apolyethylene described herein may, for example, include units derivedfrom a co-monomer that is preferably an a-olefin, e.g., propylene,1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof Otherembodiments may include dienes, ethacrylate, or methacrylate.

The term “composition” (e.g., polyethylene composition) itself broadlymeans any material that includes polyethylene, and may encompass anyblended composition that includes not only the bimodal polyethylenedescribed herein, but also other polymers and optionally additives,e.g., carbon black, and preferably includes additives used in makingpipe resin. A composition may be either a “blend” (blended) composition,which can include other polymers, e.g., other polyethylenes ornon-polyethylenes, or an “unblended” composition, which does not includeother polymers. In certain embodiments, the term “polyethylenecomposition” consists of the bimodal polyethylene alone, while in otherembodiments, the term “polyethylene composition” consists essentially ofthe bimodal polyethylene, i.e., lacking significant quantities of othermaterials, e.g., less than 5 wt % of other polymers. However, acomposition that includes non-polymer additives such as carbon black isstill regarded as a composition consisting essentially of a bimodalpolyethylene.

The term “bimodal,” when used herein to describe a polymer or polymercomposition, e.g., polyethylene, means “bimodal molecular weightdistribution,” which term is understood as having the broadestdefinition persons in the pertinent art have given that term asreflected in one or more printed publications or issued patents. Atleast one example of a bimodal polyethylene is shown in FIG. 3, in whichthe horizontal axis is expressed as the log of the molecular weight (LogMW). For example, a composition that includes a polyethylene componentwith at least one identifiable higher molecular weight and apolyethylene component with at least one identifiable lower molecularweight, e.g., two peaks (as displayed in FIG. 3), is considered to be a“bimodal” polyethylene, as that term is used herein. A material withmore than two different molecular weight distribution peaks will beconsidered “bimodal” as that term is used herein although the materialmay also be referred to as a “multimodal” composition, e.g., a trimodalor even tetramodal, etc. composition. As noted below, various differenttypes of processes, and reactor configurations, can be used to produce abimodal polyethylene composition, including melt blending, seriesreactors (i.e., sequentially-configured reactors) and single reactorsusing bimetallic catalyst systems. Any polyethylene composition regardedas a “multi-modal” composition in U.S. Pat. No. 6,579,922 is consideredto fall within the broad meaning of the term “bimodal polyethylenecomposition” herein, although important differences exist between thebimodal compositions claimed herein and the bimodal compositionsdisclosed in that patent. Thus, for example, one embodiment of bimodalcomposition is a reactor blend (also sometimes referred to as a chemicalblend), is one that is formed (polymerized) in a single reactor, e.g.,using a bimodal catalyst system (e.g., a dual site catalyst) while atleast one other embodiment of a bimodal composition is a physical blend,e.g., a composition formed by the post-polymerization blending or mixingtogether of two unimodal polyethylene compositions.

The term “bimodal catalyst system” includes any composition, mixture orsystem that includes at least two different catalyst compounds, eachhaving the same or a different metal group but generally differentligands or catalyst structure, including a “dual catalyst.”Alternatively, each different catalyst compound of the bimodal catalystsystem resides on a single support particle, e.g., in which case a dualcatalyst is considered to be a supported catalyst. However, the termbimetallic catalyst also broadly includes a system or mixture in whichone of the catalysts resides on one collection of support particles, andanother catalyst resides on another collection of support particles.Preferably, in that latter instance, the two supported catalysts areintroduced to a single reactor, either simultaneously or sequentially,and polymerization is conducted in the presence of the two collectionsof supported catalysts. Alternatively, the bimodal catalyst systemincludes a mixture of unsupported catalysts in slurry form.

The term “FI” as used herein means I₂₁, which is measured in accordancewith ASTM-1238, Condition E, at 190 degrees C.

The term “MFR (I₂₁/I₂)” as used herein means the ratio of I₂₁ (alsoreferred to as FI) to I₂, and both I₂₁ and I₂ are measured in accordancewith ASTM-1238, Condition E, at 190 degrees C.

The term “high strength” as used herein broadly refers to any one ormore of a collection of mechanical properties, e.g., strength-relatedproperties, e.g., properties used to characterize resin used in makingpipe, particularly resin that would qualify as PE-80 resin, or PE-100resin, or preferably PE-100+ resin. In at least the preferredembodiment, the high strength polyethylene compositions described hereinqualify as a PE 100 material, using any of the tests adopted by industryfor qualifying a resin in that manner. Preferably, the polyethylenecomposition is one that, in accordance with ISO 1167:1996/Cor.1:1997(E)(Technical Corrigendum 1, published 1997-03-01), entitled“Thermoplastics pipes for the conveyance of fluids—Resistance tointernal pressure—Test method,” a pipe formed from the composition thatis subjected to internal pipe resistance at selected temperatures has anextrapolated stress of 10 Mpa or greater when the internal piperesistance curve is extrapolated to 50 or 100 years in accordance withISO 9080:2003(E).

The term “high molecular weight polyethylene component” as used hereinmeans the polyethylene component in the bimodal composition that has ahigher molecular weight than the molecular weight of at least one otherpolyethylene component in the same composition. Preferably, thatpolyethylene component has an identifiable peak, e.g., as shown in FIG.3. When the composition includes more than two components, e.g., atrimodal composition, then the high molecular weight component is to bedefined as the component with the highest weight average molecularweight. In certain embodiments, a high molecular weight component is acomponent forming a part of the bimodal composition that has a weightaverage molecular weight (Mw) of from 400,000 to 700,000. In differentspecific embodiments, the average molecular weight of the high molecularweight polyethylene component may range from a low of 200,000, or250,000, or 300,000, or 350,000, or 400,000, or 450,000, or 500,000, toa high of 1,000,000, or 900,000, or 800,000, or 700,000, or 600,000.

The term “low molecular weight polyethylene component” as used hereinmeans the polyethylene component in the composition that has a lowermolecular weight than the molecular weight of at least one otherpolyethylene component in the same composition. Preferably, thatpolyethylene component has an identifiable peak, e.g., as shown in FIG.3. When the composition includes more than two components, e.g., atrimodal composition, then the low molecular weight component is to bedefined as the component with the lowest weight average molecularweight. In certain embodiments, a low molecular weight component is acomponent forming a part of the composition that has a weight averagemolecular weight (Mw) of from 15,000 to 35,000. In different specificembodiments, the average molecular weight of the low molecular weightcomponent may range from a low of 3,000, or 5,000, or 8,000, or 10,000,or 12,000, or 15,000, or 20,000, to a high of 100,000, or 50,000, or40,000, or 35,000, or 30,000.

The term “weight average molecular weight” is a term used to describe abimodal polyethylene described herein, or to describe a high molecularweight polyethylene component, and a low molecular weight polyethylenecomponent. In either case, the term “average molecular weight” broadlyrefers to any weight average molecular weight (Mw) as measured orcalculated according to any published method, which incorporatesprocedures, equipment and conditions in ASTM D 3536-91 (1991) and ASTM D5296-92 (1992).

The “overall” number average, weight average, and z-average molecularweight are terms that refer to the molecular weight values for theentire composition, as opposed to that of any individual component.Overall molecular weight values referenced in the claims encompass anyvalue as determined by any published method, including those mentionedin the paragraph above; however, a preferred method is using an SECcurve.

The number average, weight average and z-average molecular weight(particularly the weight average molecular weight) of a particularpolyethylene component recited in the claims, e.g., the high molecularweight component and the low molecular weight component, can also bedetermined any published method, including those mentioned in theparagraphs above; however, a preferred method is using any publisheddeconvolution procedure, e.g., any published technique for elucidatingeach individual component polymer's molecular information in a bimodalpolymer. A particularly preferred technique is one that uses a Florydeconvolution, including but not limited to the Flory procedures setforth in U.S. Pat. No. 6,534,604 which is incorporated by reference inits entirety. Any program that incorporates the principles contained inthe following reference is useful: P. J. Flory, Principles of PolymerChemistry, Cornell University Press, New York 1953. Any computer programcapable of fitting an experimental molecular weight distribution withmultiple Flory or log-normal statistical distributions is useful. TheFlory distribution can be expressed as follows:

$Y = {{A_{o}\left( \frac{M}{M_{n}} \right)}^{2}^{({- \frac{M}{M_{n}}})}}$

In this equation, Y is the weight fraction of polymer corresponding tothe molecular species M, Mn is the number average molecular weight ofthe distribution, and A_(o) is the weight fraction of the sitegenerating the distribution. Y can be shown to be proportional to thedifferential molecular weight distribution (DMWD) which is the change inconcentration with the change in log-molecular weight. The SECchromatogram represents the DMWD. Any computer program that minimizesthe square of the difference between the experimental and calculateddistributions by varying the A_(o) and Mn for each Flory distribution ispreferred. Particularly preferred is any program that can handle up to 8Flory distributions. A commercially available program, called ExcelSolver, offered by Frontline Systems, Inc. (Incline Village, Nev. 89450,USA) can be used to perform the minimization. Using this program,special constraints can be placed on the individual Flory distributionsthat allow one to fit chromatograms of experimental blends and bimodaldistributions.

Bimodal distributions can be fit with two individual groups of fourconstrained Flory distributions, for a total of eight distributions. Oneconstrained group of four fits the low molecular weight component whilethe other group fits the high molecular weight component. Eachconstrained group is characterized by A_(o) and Mn of the lowestmolecular weight component in the group and the ratios A_(o)(n)/A_(o)(1) and Mn(n)/Mn(1) for each of the other three distributions (n=2,3,4).Although the total number of degrees of freedom is the same for theconstrained fit as for eight unconstrained Flory distributions, thepresence of the constraint is needed to more accurately determine thecontribution to the total chromatogram of the individual low molecularweight and high molecular weight components in a bimodal polymer. Oncethe fitting process is complete, the program will then calculate themolecular weight statistics and weight percents of the individual highand low molecular weight components. FIG. 3 depicts a deconvoluted curveof each individual component.

The term “split” is defined herein as the weight % of a high molecularweight component in a bimodal composition. Thus, it describes therelative amount of the high molecular weight component against the lowmolecular weight component in a bimodal polyethylene composition,including any of the polymer compositions described herein. The weight %of each component can also be represented by the area of each molecularweight distribution curve that is seen after deconvolution of theoverall molecular weight distribution curve.

The term “spread” as used herein means the ratio of the weight averagemolecular weight of the high molecular weight polyethylene component,sometimes referred to as Mw_(HMW), to the weight average molecularweight of the low molecular weight polyethylene component, sometimesreferred to as Mw_(LMW). The “spread” can therefore be also expressed asthe ratio of Mw_(HMW):Mw_(LMW). Weight average molecular weight of eachcomponent can be obtained by deconvolution of an overall SEC curve,i.e., an SEC curve of an entire composition.

As used herein, the term “PDI” means polydispersity index, and means thesame thing as “MWD” (molecular weight distribution), which term isunderstood as having the broadest definition persons in the pertinentart have given that term as reflected in one or more printedpublications or issued patents. The PDI (MWD) is the ratio ofweight-average molecular weight (Mw) to number-average molecular weight(Mn), i.e., Mw/Mn.

As noted below, certain properties or features of the compositions,polymers, pipes, or catalyst systems are expressed in terms of lowerlimits (e.g., X or greater) or upper limits (e.g., Y or less). It isunderstood that any of the lower limits can be combined with any of theupper limits, so as to provide a variety of alternative ranges.

For any pipe produced from any one of the high strength bimodalpolyethylene compositions disclosed herein, when subjected to fullhydrostatic strength testing following ISO 1167, the extrapolated stresscan be 10 MPa or greater when extrapolated to 50 or 100 years inaccordance with ISO 9080:2003(E). Advantageously, a variety ofalternative extrapolated stress values are provided. For example, whenextrapolated to 50 or 100 years in accordance with ISO 9080:2003(E), theextrapolated stress can be 10.1 MPa or greater, or 10.2 MPa or greater,or 10.3 MPa or greater, or 10.4 MPa or greater, or 10.5 MPa or greater,or 10.6 MPa or greater, or 10.7 MPa or greater, or 10.8 MPa or greater,e.g., up to 15.0 MPa, or any combination of the foregoing upper andlower limits.

In any of the compositions described above or elsewhere herein, the meltstrength may be greater than 17 cN, greater than 18 cN, greater than 19cN, greater than 20 cN, greater than 21 cN, greater than 22 cN, greaterthan 23 cN, greater than 24 cN, greater than 25 cN, 18 cN to 30 cN, or20 cN to 30 cN, or 22 cN to 30 cN.

In any of the compositions described above or elsewhere herein, the highmolecular weight polyethylene component may have a density lower limitof 0.920 g/ml or more, or 0.925 g/ml or more, or 0.930 g/ml or more,with a density upper limit of 0.945 g/ml or less, or 0.940 g/ml or less,or 0.935 g/ml or less.

In any of the compositions described above or elsewhere herein, the lowmolecular weight polyethylene component may have a density lower limitof 0.940 g/ml or more, or 0.945 g/ml or more, or 0.950 g/ml or more,with a density upper limit of 0.965 g/ml or less, or 0.960 g/ml or less,or 0.955 g/ml or less.

In any of the compositions described above or elsewhere herein, theweight average molecular weight (Mw) of the low molecular weightpolyethylene component can be, for example, from 15,000 to 35,000, orany of the ranges spanning between other lower and upper limitsdisclosed elsewhere herein.

In any of the compositions described above or elsewhere herein, theweight average molecular weight (Mw) of the high molecular weightpolyethylene component can be, for example, from 400,000 to 700,000, orany of the ranges spanning between other lower and upper limitsdisclosed elsewhere herein.

In any of the compositions described above or elsewhere herein, the highmolecular weight polyethylene component can include a polyethylene thatincludes a comonomer being butene, hexene, octene, and mixtures thereof,wherein the comonomer is present in the amount of 1.0 wt %, orpreferably more than 2.0 wt %, or more preferably, more than 3.0 wt % ofthe polyethylene.

In any of the compositions described above or elsewhere herein, the lowmolecular weight polyethylene component can include a polyethylene thatincludes a comonomer being butene, hexene, octene, and mixtures thereof,wherein the comonomer is present in the amount of 3.0 wt %, orpreferably less than 2.0 wt %, or more preferably, less than 1.0 wt % ofthe polyethylene.

In one or more of the high strength compositions disclosed herein, theweight % of high molecular weight polyethylene component, can occupy 45wt % or more of the composition, also termed the “split” as discussedabove. In alternative embodiments, the high molecular weightpolyethylene component can occupy 46 wt % or more, 47 wt % or more, 48wt % or more, 49 wt % or more, or 50 wt % or more of the composition.Conversely, in any of those aforementioned high strength compositions,the high molecular weight polyethylene component can occupy 60 wt % orless of the composition, or 59 wt % or less, 58 wt % or less, 57 wt % orless, 56 wt % or less, 55 wt % or less, 54 wt % or less, 53 wt % orless, or 52 wt % or less, or any combination of the foregoing upper andlower limits. In certain embodiments, the split is 45 wt % to 60 wt %,48 wt % to 56 wt %, 50 wt % to 52 wt %, or 51 wt %.

In one or more of the high strength compositions disclosed herein, thespread, the ratio of Mw_(HMW):Mw_(LMW) as defined previously, can be 15or more, 17 or more, 19 or more, 21 or more, 40 or less, 36 or less, 32or less, 28 or less, 25 or less, or any combination of the foregoingupper and lower limits, or 15 to 40, 17 to 35, 19 to 29, 21 to 23, or22.

In one or more of the high strength compositions disclosed herein, theFI (I₂₁) of the composition can range from 4 to 10 g/10 min. Inalternative embodiments, the FI can be expressed as having any one of anumber of ranges, e.g., with a lower limit of 4 g/10 min or above, or 5g/10 min or above, or 6 g/10 min or above, or 7 g/10 min or above, or 8g/10 min or above, or 9 g/10 min or above; together with an upper limitof 10 g/10 min or below, or 9 g/10 min or below, or 8 g/10 min or below,or 7 g/10 min or below, or 6 g/10 min or below, or 5 g/10 min or below,or any combination of the foregoing upper and lower limits. In oneembodiment, the FI is 4 to 10 g/10 min.

In one or more of the high strength compositions disclosed herein, theMFR (I₂₁/I₂) can range from 100 to 250. In alternative embodiments, theMFR can be expressed as having any one of a number of ranges, e.g., witha lower limit of 50, or 60, or 70, or 80, or 90, or 100, or 110, or 120,or 130, or 140, or 150; together with an upper limit of 150, or 180, or200, or 220, or 250, or 270, or 300, or 320, or 350, or any combinationof the foregoing upper and lower limits.

In one or more of the high strength compositions disclosed herein, thePDI of the overall composition can be expressed as having any one of anumber of ranges, e.g., with a lower limit of 10, or 15; together withan upper limit of 45 or less, or 40 or less, or 35 or less, or 30 orless, or 25 or less or any combination of the foregoing upper and lowerlimits. In certain embodiments, the PDI can be 15 to 40, or 17 to 31, or19 to 22, or 20.

In one or more of the high strength compositions disclosed herein, thePDI of the high molecular weight component can be greater than 3.5. Inalternative embodiments, the PDI of the high molecular weight componentcan be expressed as having any one of a number of ranges, e.g., with alower limit of 3.0 or more, or 3.5 or more, or 4.0 or more, or 4.5 ormore, or 5.0 or more, or 5.5 or more or 6.0 or more, together with anupper limit of 6.0 or less, or a combination of the foregoing upper andlower limits.

In one or more of the high strength compositions disclosed herein, thePDI of the low molecular weight component can be 2.5 or more. Inalternative embodiments, the PDI of the low molecular weight componentcan be expressed as having any number of ranges, e.g., with a lowerlimit of 2.0 or more, or 2.5 or more, or 3.0 or more, or 3.5 or more,or; together with an upper limit of 5.0 or less, or 4.5 or less, or 4.0or less, or 3.5 or lesser any combination of the foregoing upper andlower limits.

In one or more of the high strength compositions disclosed herein, theaverage molecular weight of the overall composition can be 200,000 ormore. In alternative embodiments, the average molecular weight of theoverall composition can be expressed as having any one of a number ofranges, e.g., with a lower limit of 50,000 or more, or 100,000 or more,or 150,000 or more, or 200,000 or more, or 250,000 or more, or 300,000or more, or 350,000 or more, or 400,000 or more, or 450,000 or more;together with an upper limit of 1,000,000 or less, or 900,000 or less,or 850,000 or less, or 800,000 or less, or 750,000 or less, or 700,000or less, or 650,000 or less, or 600,000 or less, or 550,000 or less, or500,000 or less, or 450,000 or less, or 400,000 or less or anycombination of the foregoing upper and lower limits.

In one or more of the high strength compositions disclosed herein, theaverage molecular weight (Mw) of the low molecular weight component ispreferably 15,000 or more; or 18,000 or more; or 22,000 or more; and ispreferably 35,000 or less; or 32,000 or less; or 28,000 or less, orranges represented by any combination of the foregoing upper and lowerlimits. In certain embodiments, the Mw of the low molecular weightcomponent can be 15,000 to 35,000, or 25,000.

In one or more of the high strength compositions disclosed herein, thehigh and low molecular weight polyethylene components can be formed in asingle reactor. Examples of such reactors are disclosed elsewhere hereinin greater detail.

In one or more of the high strength compositions disclosed herein, thehigh and low molecular weight polyethylene components can be formed ingas phase polymerization. Details of useful gas phase polymerizationsare described elsewhere herein.

One or more of the high strength compositions disclosed herein can bemade from polymerization conducted in the presence of a bimodal catalystsystem that includes a metallocene based catalyst.

In one or more of the high strength compositions disclosed herein, thehigh and low molecular weight polyethylene components can be formed frompolymerization conducted in the presence of a bimodal catalyst systemthat includes bis(2-(trimethylphenylamido)ethyl)amine zirconiumdibenzyl.

In one or more of the high strength compositions disclosed herein, thehigh and low molecular weight polyethylene components can be formed frompolymerization conducted in the presence of a bimodal catalyst systemthat includes bis(2-(pentamethylphenylamido)ethyl)amine zirconiumdibenzyl.

In one or more of the high strength compositions disclosed herein, thehigh and low molecular weight polyethylene components can be formed frompolymerization conducted in the presence of a bimodal catalyst systemthat includes(pentamethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdichloride.

In one or more of the high strength compositions disclosed herein, thehigh and low molecular weight polyethylene components can be formed frompolymerization conducted in the presence of a bimodal catalyst systemthat includes(tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdichloride or(tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdimethyl.

In one or more of the high strength compositions disclosed herein, thehigh and low molecular weight polyethylene components can be formed frompolymerization conducted in the presence of a bimodal catalyst systemthat includes bis(n-butylcyclopentadienyl)zirconium dichloride orbis(n-butylcyclopentadienyl)zirconium dimethyl.

Bimodal Polyethylene Compositions

As noted above, the high strength bimodal polyethylene compositionpreferably has a density of 0.940 g/cc or more, and includes (and incertain embodiments consists or consists essentially of) a highmolecular weight polyethylene component having a higher weight averagemolecular weight (Mw_(HMW)) and a low molecular weight polyethylenecomponent having a lower weight average molecular weight (Mw_(LMW)),wherein: the composition qualifies as a PE 100 material such that inaccordance with ISO 1167 a pipe formed from the composition that issubjected to internal pipe resistance has an extrapolated stress of 10MPa or more when the internal pipe resistance curve is extrapolated to50 or 100 years in accordance with ISO 9080:2003(E); and the meltstrength is greater than 18 cN. As noted in the discussion of thespecific embodiments; likewise, the extrapolated stress can be higher,and is preferably 10.5 MPa or higher, and even 10.7 MPa or higher.

In at least one particular embodiment, a composition includes a bimodalpolyethylene composition prepared using any of the catalyst systemsdescribed above but, not limited to those illustrated herein.

As noted above, the bimodal polyethylene compositions preferably have ahigh molecular weight component and a low molecular weight component.Preferably, the high molecular weight component has a lower density thanthe density of the low molecular weight component. Also, the highmolecular weight component preferably has a higher comonomer contentthan the comonomer content of the low molecular weight component. Thecomonomer content can be expressed as the number of comonomer branchesper 1000 carbon atoms. In certain embodiments, the number of comonomerbranches per 1000 carbon atoms for the low molecular weight component isbetween 0 and 2, preferably 1 or less. In certain embodiments, thenumber of comonomer branches per 1000 carbon atoms for the highmolecular weight component is 2 to 5, preferably more than 2, or morepreferably, more than 3.

Polymerization Processes

The polymerization process used to form any of the polymers describedherein, may be carried out using any suitable process, for example, highpressure, solution, slurry and gas phase. Certain polyethylenes can bemade using a gas phase polymerization process, e.g., utilizing afluidized bed reactor. This type reactor and means for operating thereactor are well known and completely described in, for example, U.S.Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,302,566; 4,543,399;4,882,400; 5,352,749; 5,541,270; EP-A-0 802 202 and Belgian Patent No.839,380. These patents disclose gas phase polymerization processeswherein the polymerization medium is either mechanically agitated orfluidized by the continuous flow of the gaseous monomer and diluent.

A polymerization process may be effected as a continuous gas phaseprocess such as a fluid bed process. A fluid bed reactor may comprise areaction zone and a so-called velocity reduction zone. The reaction zonemay comprise a bed of growing polymer particles, formed polymerparticles and a minor amount of catalyst particles fluidized by thecontinuous flow of the gaseous monomer and diluent to remove heat ofpolymerization through the reaction zone. Optionally, some of there-circulated gases may be cooled and compressed to form liquids thatincrease the heat removal capacity of the circulating gas stream whenreadmitted to the reaction zone. A suitable rate of gas flow may bereadily determined by simple experiment. Make up of gaseous monomer tothe circulating gas stream is at a rate equal to the rate at whichparticulate polymer product and monomer associated therewith iswithdrawn from the reactor and the composition of the gas passingthrough the reactor is adjusted to maintain an essentially steady stategaseous composition within the reaction zone. The gas leaving thereaction zone is passed to the velocity reduction zone where entrainedparticles are removed. Finer entrained particles and dust may optionallybe removed in a cyclone and/or fine filter. The gas is passed through aheat exchanger wherein the heat of polymerization is removed, compressedin a compressor and then returned to the reaction zone.

The reactor temperature of the fluid bed process herein preferablyranges from 30° C. or 40° C. or 50° C. to 90° C. or 100° C. or 110° C.or 120° C. In general, the reactor temperature is operated at thehighest temperature that is feasible taking into account the sinteringtemperature of the polymer product within the reactor. Regardless of theprocess used to make the polyolefins of the invention, thepolymerization temperature, or reaction temperature should be below themelting or “sintering” temperature of the polymer to be formed. Thus,the upper temperature limit in one embodiment is the melting temperatureof the polyolefin produced in the reactor.

A slurry polymerization process can also be used. A slurrypolymerization process generally uses pressures in the range of from 1to 50 atmospheres and even greater and temperatures in the range of 0°C. to 120° C., and more particularly from 30° C. to 100° C. In a slurrypolymerization, a suspension of solid, particulate polymer is formed ina liquid polymerization diluent medium to which ethylene and comonomersand often hydrogen along with catalyst are added. The suspensionincluding diluent is intermittently or continuously removed from thereactor where the volatile components are separated from the polymer andrecycled, optionally after a distillation, to the reactor. The liquiddiluent employed in the polymerization medium is typically an alkanehaving from 3 to 7 carbon atoms, a branched alkane in one embodiment.The medium employed should be liquid under the conditions ofpolymerization and relatively inert. When a propane medium is used theprocess must be operated above the reaction diluent critical temperatureand pressure. In one embodiment, a hexane, isopentane or isobutanemedium is employed.

Also useful is particle form polymerization, a process where thetemperature is kept below the temperature at which the polymer goes intosolution. Other slurry processes include those employing a loop reactorand those utilizing a plurality of stirred reactors in series, parallel,or combinations thereof Non-limiting examples of slurry processesinclude continuous loop or stirred tank processes. Also, other examplesof slurry processes are described in U.S. Pat. No. 4,613,484 and 2Metallocene-Based Polyolefins 322-332 (2000).

These processes can be used for the production of homopolymers ofolefins, particularly ethylene, and/or copolymers, terpolymers, and thelike, of olefins, particularly ethylene, and at least one or more otherolefin(s). Preferably the olefins are α-olefins. The olefins, forexample, may contain from 2 to 16 carbon atoms in one embodiment; and inanother embodiment, ethylene and a comonomer comprising from 3 to 12carbon atoms in another embodiment; and ethylene and a comonomercomprising from 4 to 10 carbon atoms in yet another embodiment; andethylene and a comonomer comprising from 4 to 8 carbon atoms in yetanother embodiment. Particularly preferred are polyethylenes. Suchpolyethylenes are preferably homopolymers of ethylene and interpolymersof ethylene and at least one α-olefin wherein the ethylene content is atleast about 50% by weight of the total monomers involved. Exemplaryolefins that may be utilized herein are ethylene, propylene, 1-butene,1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene,1-dodecene, 1-hexadecene and the like. Also utilizable herein arepolyenes such as 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene,dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene,5-vinylidene-2-norbornene and 5-vinyl-2-norbornene, and olefins formedin situ in the polymerization medium. When olefins are formed in situ inthe polymerization medium, the formation of polyolefins containing longchain branching may occur.

In the production of polyethylene or polypropylene, comonomers may bepresent in the polymerization reactor. When present, the comonomer maybe present at any level with the ethylene or propylene monomer that willachieve the desired weight percent incorporation of the comonomer intothe finished resin. In one embodiment of polyethylene production, thecomonomer is present with ethylene in a mole ratio range of from 0.0001(comonomer:ethylene) to 50, and from 0.0001 to 5 in another embodiment,and from 0.0005 to 1.0 in yet another embodiment, and from 0.001 to 0.5in yet another embodiment. Expressed in absolute terms, in makingpolyethylene, the amount of ethylene present in the polymerizationreactor may range to up to 1000 atmospheres pressure in one embodiment,and up to 500 atmospheres pressure in another embodiment, and up to 200atmospheres pressure in yet another embodiment, and up to 100atmospheres in yet another embodiment, and up to 50 atmospheres in yetanother embodiment.

Hydrogen gas is often used in olefin polymerization to control the finalproperties of the polyolefin, such as described in PolypropyleneHandbook 76-78 (Hanser Publishers, 1996). Using certain catalystsystems, increasing concentrations (partial pressures) of hydrogen canincrease the melt flow rate (MFR) (also referred to herein as melt index(MI)) of the polyolefin generated. The MFR or MI can thus be influencedby the hydrogen concentration. The amount of hydrogen in thepolymerization can be expressed as a mole ratio relative to the totalpolymerizable monomer, for example, ethylene, or a blend of ethylene andhexene, propene, pentene, octene, and mixtures thereof The amount ofhydrogen used in the polymerization process of the present invention isan amount necessary to achieve the desired MFR or MI of the finalpolyolefin resin. In one embodiment, the mole ratio of hydrogen to totalmonomer (H₂:monomer) is in a range of from greater than 0.0001 in oneembodiment, and from greater than 0.0005 in another embodiment, and fromgreater than 0.001 in yet another embodiment, and less than 10 in yetanother embodiment, and less than 5 in yet another embodiment, and lessthan 3 in yet another embodiment, and less than 0.10 in yet anotherembodiment, wherein a desirable range may comprise any combination ofany upper mole ratio limit with any lower mole ratio limit describedherein. Expressed another way, the amount of hydrogen in the reactor atany time may range to up to 5000 ppm, and up to 4000 ppm in anotherembodiment, and up to 3000 ppm in yet another embodiment, and between 50ppm and 5000 ppm in yet another embodiment, and between 500 ppm and 2000ppm in another embodiment.

Further, it is common to use a staged reactor employing two or morereactors in series, wherein one reactor may produce, for example, a highmolecular weight component and another reactor may produce a lowmolecular weight component. In one embodiment of the invention, thepolyolefin is produced using a staged gas phase reactor. Such commercialpolymerization systems are described in, for example, 2Metallocene-Based Polyolefins 366-378 (John Scheirs & W. Kaminsky, eds.John Wiley & Sons, Ltd. 2000); U.S. Pat. No. 5,665,818, U.S. Pat. No.5,677,375; U.S. Pat. No. 6,472,484; EP 0 517 868 and EP-A-0 794 200.

The one or more reactor pressures in a gas phase process (either singlestage or two or more stages) may vary from 100 psig (690 kPa) to 500psig (3448 kPa), and in the range of from 200 psig (1379 kPa) to 400psig (2759 kPa) in another embodiment, and in the range of from 250 psig(1724 kPa) to 350 psig (2414 kPa) in yet another embodiment.

The gas phase reactor employing the catalyst system described herein iscapable of producing from 500 lbs of polymer per hour (227 Kg/hr) to200,000 lbs/hr (90,900 Kg/hr), and greater than 1000 lbs/hr (455 Kg/hr)in another embodiment, and greater than 10,000 lbs/hr (4540 Kg/hr) inyet another embodiment, and greater than 25,000 lbs/hr (11,300 Kg/hr) inyet another embodiment, and greater than 35,000 lbs/hr (15,900 Kg/hr) inyet another embodiment, and greater than 50,000 lbs/hr (22,700 Kg/hr) inyet another embodiment, and from 65,000 lbs/hr (29,000 Kg/hr) to 100,000lbs/hr (45,500 Kg/hr) in yet another embodiment.

A slurry or gas phase process can be operated in the presence of ametallocene-type catalyst system and in the absence of, or essentiallyfree of, any scavengers, such as triethylaluminum, trimethylaluminum,tri-isobutylaluminum and tri-n-hexylaluminum and diethyl aluminumchloride, dibutyl zinc and the like. By “essentially free”, it is meantthat these compounds are not deliberately added to the reactor or anyreactor components, and if present, are present to less than 1 ppm inthe reactor.

One or all of the catalysts can be combined with up to 10 wt % of ametal-fatty acid compound, such as, for example, an aluminum stearate,based upon the weight of the catalyst system (or its components), suchas disclosed in U.S. Pat. Nos. 6,300,436 and 5,283,278. Other suitablemetals include other Group 2 and Group 5-13 metals. In an alternativeembodiment, a solution of the metal-fatty acid compound is fed into thereactor. In yet another embodiment, the metal-fatty acid compound ismixed with the catalyst and fed into the reactor separately. Theseagents may be mixed with the catalyst or may be fed into the reactor ina solution or a slurry with or without the catalyst system or itscomponents.

Supported catalyst(s) can be combined with the activators and arecombined, such as by tumbling and other suitable means, with up to 2.5wt % (by weight of the catalyst composition) of an antistatic agent,such as an ethoxylated or methoxylated amine, an example of which isKemamine AS-990 (ICI Specialties, Bloomington Delaware).

EXAMPLES

It is to be understood that while the invention has been described inconjunction with the specific embodiments thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention. Other aspects, advantages and modifications will be apparentto those skilled in the art to which the invention pertains.

Therefore, the following examples are put forth so as to provide thoseskilled in the art with a complete disclosure and description of how tomake and use the compounds of the invention, and are not intended tolimit the scope of that which the inventors regard as their invention.

The following examples discuss some properties and other characteristicsof bimodal polyethylene compositions that qualify as a PE 100 materialand have, among other things, surprisingly high melt strength.

TABLE 1 Properties of a composition according to an embodiment of theinstant invention and of four commercial compositions. η*_(0.01)/ ID #Resin process I₂₁ I₅ I₂ I₂₁/I₂ I₂₁/I₅ density η*_(0.01) η*_(0.1)η*_(0.1) UCUT- Qenos HDF- Hostalen ™ 8.8 0.32 0.07 133 27.0 0.94772.24E+05 1.05E+05 2.13 1148-67- 193 ™ 193 1163-4- Atofina dual slurry7.6 0.31 0.07 105 24.6 — 2.01E+05 1.11E+05 1.81 XS10 XS10H ™ loop1163-4- Borealis gas-phase- 9.0 0.38 0.09 100 23.9 — 1.15E+05 6.97E+041.65 349 HE3490 ™ slurry 1163-4- Borealis gas-phase- 8.9 0.28 0.06 15931.3 — 2.35E+05 1.14E+05 2.06 349LS HE3490 LS ™ slurry 1163-4- CRP 100 ™Hostalen ™ 5.7 0.24 0.06 88 23.2 — 1.91E+05 1.03E+05 1.85 CRP100 Pipe1163- PRODIGY ™ Unipol ™ 5.943 0.15 0.03 196.6 40.5 0.9494 4.41E+052.14E+05 2.06 18-1 BMC-200 (inventive)

Referring to Tables 1 and 2, Qenos HDF-193™ is available from Qenos PtyLtd., Altona, Victotia, Australia. Atofina XS10H™ is available fromArkema Canada, Oakville, Ontario, Canada. Borealis HE3490™ and BorialisHE3490 LS™ are available from Borealis Polymers Oy, Porvoo, Finland(“LS” refers to “Low Sag”). CRP 100 Pipe™ is available fromLyondellBasell Industries, Rotterdam, The Netherlands.

TABLE 2 Properties of a composition according to an embodiment of theinstant invention and of four commercial compositions. ID # Resin LMW MwHMW Mw split, % spread Mn Mw Mw/Mn UCUT- Qenos HDF- 38,656 643,821 42.616.7 17,342 301,313 17.4 1148-67- 193 ™ 193 1163-4- Atofina 25,947417,118 63.5 16.1 21,437 281,315 13.1 XS10 XS10H ™ 1163-4- Borealis21,693 378,286 63.1 17.4 16,640 252,014 15.1 349 HE3490 ™ 1163-4-Borealis 25,804 506,181 57.6 19.6 18,584 313,353 16.9 349LS HE3490 LS ™1163-4- CRP 100 ™ 22,497 449,248 67.2 20.0 21,861 320,914 14.7 CRP100Pipe 1163- PRODIGY ™ 24,357 549,914 52.5 22.6 13,341 312,290 23.4 18-1BMC-200 (inventive)

FIG. 1 is a graph showing the dynamic viscosity of three samplesaccording to embodiments of the instant invention (all designated as1163-18-1 since the same conditions were present, the samples beingtaken at different times) and of five commercial samples. Dynamicviscosity was measured using a Rheometrics (Piscatway, N.J., U.S.)dynamic stress rheometer, model SR-200 at 190° C. and at a shearing raterange of 0.01 to 100 s⁻¹.

FIG. 2 is a graph showing the Rheotens melt strength versus pull-offspeed for two samples according to embodiments of the instant inventionand of four commercial samples. Melt strength was measured using aGottFert (Rock Hill S.C., U.S.) Rheo-Tester 2000 under the followingconditions: Instrument: Gottfert Rheo-Tester 2000; test temperature:190° C.; die length/diameter: 20 mm/2 mm; barrel diameter: 15 mm; startspeed: 9.5 mm/s; acceleration: 2 4 mm/s₂; strand length between die androllers: 130 mm; and gap between rollers: 0.5 mm.

Example 1

Bimodal polyethylene resin products, henceforth referred to as the“Bimodal Product,” was produced using gas phase polymerization in asingle-reactor system with a spray-dried catalyst system that includedbis(2-pentamethylphenylamido)ethyl)zirconium dibenzyl together with(tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdichloride in a 3.0:1 molar ratio. Such catalyst systems arecommercially available from Univation Technologies, LLC (Houston, Tex.)and sold under PRODIGY™ Bimodal Catalysts. Also fed to the reactor wasMMAO, a modified methylalumoxane. A “dry mode” was utilized, meaningthat the material was introduced in the form of dry powder (granules).The resulting Bimodal Products samples had an FI of 5-7; a densityranging from 0.947 to 0.950; and MFR of approximately 170-200.Representative reactor conditions for the product are summarized inTable 3 Bed weight=34,000 lbs.; Fluidized bulk density=13-19 lb/ft3;SGV=2 to 2.15 ft/s; Dew point=55 to 60 ° C.; IC₅=10 to 12%.

TABLE 3 Reaction Conditions C₂ partial pressure ID # Resin psi T_(rx)°C. H₂/C₂ C₆/C₂ 1163-18-1 PRODIGY ™ 220 105 0.0021 0.0041 BMC-2001148-93-3B PRODIGY ™ 220 105 0.0020 0.0060 BMC-200 1163-34-1 PRODIGY ™220 100 0.0021 0.0045 BMC-200

Resin Properties

Compounded granular samples of Bimodal Product resin were prepared, onKobe LCM-100 compounding line (Kobe Steel, Ltd., Hyogo Japan) equippedwith EL-2 rotors, using compounding additives, namely, 2,000 ppm ofB-225 (Irganox™ 1010 and Irgafos™ 168 in a 1:1 ratio) and 500 ppm ofCaSt. Carbon black was incorporated at 2.25 wt % through a masterbatch.The resulting pellet samples were measured for flow properties, density,and Size Exclusion Chromatography (SEC), as discussed below.

Table 4 presents flow properties of two samples of Bimodal Product.Sample 1163-18-1 was a Bimodal Product compounded without carbon black,a natural grade (NG) bimodal product produced from a dry catalyst system(identified above). Sample 1163-18-1 BK was a bimodal product thatincluded black compounds but was otherwise identical to Sample1163-18-1. The black compounds were masterbatches containing carbonblack. Note that addition of black compounds had little impact on theoverall flow properties, but density increased about 0.01 g/cc andresulted in a density of approximately 0.9597 g/cc.

TABLE 4 Flow Properties Sample ID # FI (I₂₁) MI (I₂) MFR (I₂₁/I₂)Density (g/cc) 1163-18-1 5.9 0.03 197 0.9494 1163-18-1 BK 6.65 0.033 1990.9597 1148-93-3B 5.3 .031 172 0.9471 1163-34-1 5.5 .028 195 0.9488

Characteristics

FIG. 3 shows a molecular weight distribution (MWD) curve taken of theBimodal Product (sample 1163-18-1) using the SEC technique describedherein (GPC method), which reveals two peaks, one of which correspondsto a relatively low molecular weight component, the other correspondingto a high molecular weight component. Table 5 below shows molecular datafrom SEC and its deconvolution results for these samples. The overallMw's range from approximately 312,000 to 415,000 and the overall Mn'srange from approximately 13,000 to 14,500. Overall polydispersity (PDI)was 23.4 to 28.5. The HMW component weight %, or split, was 52-53 wt %,and the PDI of the HMW component was 4.7. The “spread,” i.e., the ratioof Mw_(HMW) to Mw_(LMW), was 22.6.

TABLE 5 Molecular Data Property 1163-18-1 1148-93-3B 1163-34-1 Mw_L24,357 23,273 22,800 Mw_H 549,914 534,513 764,779 split 52.5 52.8 52.5spread 22.6 23 33.5 Mn 13,341 11,039 14,534 Mw 312,290 292,969 414,867DI 23.4 26.5 28.5

Slow Crack Growth Performance

The slow crack growth performance was tested using the notched pipetest, ISO 13479. The notched pipe SCG test was 4 inch SDR11 pipe. Thetest conditions used were 80° C. and 9.2 bars pressure. The averagefailure time for three specimens of sample 1163-18-1 was 3,672 hrs,exceeding the PE-100 requirement of ≧500 hrs.

Test specimens of specific dimensions for Pennsylvania notch test (PENT)and Charpy impact test were prepared for sample 1163-18-1. PENT (ASTMF1473-94) is a lab-scale screening test with small specimens to predictthe resistance of slow crack growth of pipes. Samples of the BimodalProduct, in pellet resin form, were compression molded to make plaquesfor PENT in accordance with the ASTM standard. From the plaques, threerectangular specimens were milled, cut and then placed onto PENT teststations.

Two specimens made from the same batch of Bimodal Product sample1163-18-1 lasted between 1,800 and 2,600 hrs.

Pipe Extrusion Testing

Then, pipes were extruded for purposes of a long-term hydrostatic testin an external test laboratory. The pipe extruder was a Maplan modelSS60-30. The molten pipe profile coming out of an annular die was drawndown from the die-gap opening into the interior of the sizing sleeve bya puller located further downstream. As pipe moved through the sizingsleeve, a vacuum pulled the molten profile against the interior of thesleeve. Cooling water entered the compartment, cooling the pipe andmaintaining established dimensions. Nominal 32 mm SDR 11 pipes of highquality with smooth surface were produced.

Short Term Hydrostatic Strength Tests of Pipes

Standardized internal pressure tests for plastic pipe are set forth inISO 1167 entitled “Thermoplastic pipes for the conveyance offluids—Resistance to internal pressure—Test method.” The test specifiesa method for determination of the resistance to constant internalpressure at constant temperature. The test requires that samples be keptin an environment at a specific temperature, which can be water(“water-in-water” test), another liquid (“water-in-liquid”) or air(“water-in-air” test).

Hydrostatic testing was performed, as described in ISO 4437, table 8following ISO 1167. This test is a short-term screening hydrostaticpressure test being conducted at three specific hydrostatic conditions.ISO 4437 specifies three specific criteria for PE-80 and PE-100 resins.The tests were performed on 32 mm SDR 11 pipes (3mm thickness) as“water-in-water” test. In terms of pipe length, the standard requires atleast three times the outside diameter. In our case, the length of pipewas 350 mm.

Pipe specimens made from Bimodal Product (sample 1163-18-1, whichincludes carbon black, called sample 1163-18-1 BK) were subjected to thethree conditions required for PE-100. Table 6 reveals the test resultsfor short-term hydrostatic strength tests as described in ISO 4437following ISO 1167 for pipe specimens made from sample 1163-18-1 BK.

TABLE 6 Hydrostatic strength Require- Pipe Hydrostatic Failure ments onTest parameters Specimen Temp pressure time failure for PE-100 numbers °C. (Mpa) (Hour) time pipe resin 1 20 12.4 341 ≧100 @20° C. and 12.4 MPa2 80 5.41 >5,400 ≧165 @80° C. and 5.4 MPa 7 80 5.05 >5,400 ≧1,000 @80°C. and 5.0 Mpa

It should be noted that, for all the cases, sample 1163-18-1 BK farexceeded the failure-time criteria for PE-100 that is specified in ISO4437.

The phrases, unless otherwise specified, “consists essentially of” and“consisting essentially of” do not exclude the presence of other steps,elements, or materials, whether or not, specifically mentioned in thisspecification, so long as such steps, elements, or materials, do notaffect the basic and novel characteristics of the invention,additionally, they do not exclude impurities and variances normallyassociated with the elements and materials used.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, within a range includes everypoint or individual value between its end points even though notexplicitly recited. Thus, every point or individual value may serve asits own lower or upper limit combined with any other point or individualvalue or any other lower or upper limit, to recite a range notexplicitly recited.

All priority documents are herein fully incorporated by reference forall jurisdictions in which such incorporation is permitted and to theextent such disclosure is consistent with the description of the presentinvention. Further, all documents and references cited herein, includingtesting procedures, publications, patents, journal articles, etc. areherein fully incorporated by reference for all jurisdictions in whichsuch incorporation is permitted and to the extent such disclosure isconsistent with the description of the present invention.

While the invention has been described with respect to a number ofembodiments and examples, those skilled in the art, having benefit ofthis disclosure, will appreciate that other embodiments can be devisedwhich do not depart from the scope and spirit of the invention asdisclosed herein.

1. A bimodal polyethylene composition having a density of 0.940 g/cc ormore, the composition comprising a high molecular weight polyethylenecomponent and a low molecular weight polyethylene component, wherein:the composition qualifies as a PE 100 material such that in accordancewith ISO 1167 a pipe formed from the composition that is subjected tointernal pipe resistance has an extrapolated stress of 10 MPa or morewhen the internal pipe resistance curve is extrapolated to 50 or 100years in accordance with ISO 9080:2003(E); and the composition has amelt strength of 18 cN or greater.
 2. The composition of claim 1 whereinthe high and low molecular weight polyethylene components are formed ina single reactor.
 3. The composition of any one of the preceding claimsin which the melt strength is greater than 20 cN.
 4. The composition anyone of the preceding claims in which the melt strength is greater than22 cN.
 5. The composition of any one of the preceding claims in whichthe complex viscosity at 0.01 s-1 is greater than 3.5*105 Pa-s.
 6. Thecomposition of any one of the preceding claims in which the complexviscosity at 0.1 s-1 is greater than 1.5*105 Pa-s.
 7. The composition ofany one of the preceding claims having an overall PDI of 15 to
 40. 8.The composition of any one of the preceding claims in which the highmolecular weight component is present in an amount of 45 to 60 wt. %. 9.The composition of any one of the preceding claims in which the averagemolecular weight (Mw) of the low molecular weight polyethylene componentis from 5,000 to 35,000.
 10. The composition of any one of the precedingclaims in which the average molecular weight (Mw) of the high molecularweight polyethylene component is from 400,000 to 700,000.
 11. Thecomposition of any one of the preceding claims in which the ratio of theweight average molecular weight of high molecular weight component tothe weight average molecular weight of low molecular weight component(MwHMW:MwLMW) is 15 to 40:1.
 12. The composition of any one of thepreceding claims having an FI (I21) of from 4 to 10 g/10 min.
 13. Thecomposition of any one of the preceding claims in which the highmolecular weight polyethylene component has a density of 0.945 or less.14. The composition of any one of the preceding claims in which the lowmolecular weight polyethylene component has a density of 0.940 or more.15. The composition of any one of the preceding claims in which the highmolecular weight polyethylene component comprises a polyethylene thatcomprises a comonomer being butene, hexene, octene, and mixturesthereof, wherein the comonomer is present in the amount of more than 1.0wt % of the polyethylene.
 16. The composition of any one of thepreceding claims in which the low molecular weight polyethylenecomponent comprises a polyethylene that comprises a comonomer beingbutene, hexene, octene, and mixtures thereof, wherein the comonomer ispresent in the amount of less than 3.0 wt % of the polyethylene.
 17. Thecomposition of any one of the preceding claims wherein the extrapolatedstress is 10.5 MPa or more when extrapolated to 50 or 100 years inaccordance with ISO 9080:2003(E).
 18. The composition of any one of thepreceding claims or any one of claims 20-25 wherein the high and lowmolecular weight polyethylene components are formed in gas phasepolymerization.
 19. The composition of any one of claim 1-17 or 20-25wherein the high and low molecular weight polyethylene components areformed in slurry phase polymerization.
 20. The composition of any one ofthe preceding claims wherein the composition is made from polymerizationconducted in the presence of a bimodal catalyst system that comprises ametallocene based catalyst.
 21. The composition of any one of thepreceding claims wherein the high and low molecular weight polyethylenecomponents are formed from polymerization conducted in the presence of abimodal catalyst system that comprisesbis(2-trymethylphenylamido)ethyl)amine zirconium dibenzyl.
 22. Thecomposition of any one of the preceding claims wherein the high and lowmolecular weight polyethylene components are formed from polymerizationconducted in the presence of a bimodal catalyst system that comprisesbis(2-(pentamethyl-phenylamido)ethyl)amine zirconium dibenzyl.
 23. Thecomposition of any one of the preceding claims wherein the high and lowmolecular weight polyethylene components are formed from polymerizationconducted in the presence of a bimodal catalyst system that comprises(pentamethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdichloride.
 24. The composition of any one of the preceding claimswherein the high and low molecular weight polyethylene components areformed from polymerization conducted in the presence of a bimodalcatalyst system that comprises(tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdichloride or(tetramethylcyclopentadienyl)(n-propylcyclopentadienyl)zirconiumdimethyl.
 25. The composition of any one of the preceding claims whereinthe high and low molecular weight polyethylene components are formedfrom polymerization conducted in the presence of a bimodal catalystsystem that comprises bis(2-pentamethylphenylamido)ethyl)zirconiumdibenzyl or bis(2-pentamethylphenylamido)ethyl)zirconium dimethyl.